The present invention relates to a peripheral length correction device of metal rings, and more particularly to a peripheral length correction device used to correct the peripheral length of metal rings which constitute a V-belt type continuously variable transmission belt (hereinafter referred to as “CVT belt”).
Conventionally, there is a known CVT belt which is structured by layering about ten thin metal rings of 0.2 mm thickness in succession with steel metal elements inserted therein. For example, as disclosed in “REALIZATION OF THE IDEAL MAXIMUM PERFORMANCE OF A CVT TRANSMISSION” by Tomomi Miyaji, [on line], [searched on Aug. 25, 2002], Internet <URL: http://www.idemitsu.co.jp/lube/cvtbody2.html> and illustrated in FIG. 4 of this homepage.
The CVT belt of such a structure is manufactured as follows. First, the ends of the thin sheet metal, which are made of super strong steel such as maraging steel, are welded together to form a ring-shaped drum. The drum is then cut into the predetermined width and rolled out to constitute metal rings of a predetermined peripheral length. The metal rings are then subjected to a solution treatment or the like. This is followed by a peripheral length correction process, which is carried out by a “peripheral length correction device” to correct the metal rings to an accurate peripheral length. The metal rings are further subjected to an aging treatment, nitriding and the like to enhance their hardness. A plurality of such metal rings (about ten mentioned above) which vary slightly in peripheral length from one to the other are mutually layered to form a CVT belt. Thus, the peripheral length correction device is an important and indispensable device to carry out the lamination of multiple thin metal rings to form one CVT belt.
As a conventional peripheral length correction device, there is known device which carries a solution treated and the like metal rings (hereinafter referred to as “receiving correction rings”) laid on two rollers (driving roller and driven roller) of which either or both are displaceable in mutually separating directions while rotating the rollers, and thereby applying tensile stress to the receiving correction rings to correct their peripheral length. This device is described in Japanese Laid-Open (Kokai) Patent Application (A) numbered 2001-105050 titled “METHOD FOR PERIPHERAL LENGTH CORRECTION OF METAL RINGS.”
The conventional peripheral length correction device is useful in that each of the number of metal rings constituting a CVT belt is corrected to a shorter peripheral length for the inner side of the metal ring and a longer peripheral length for the outer side of the metal ring. Therefore, the necessary peripheral length difference for layering the metal rings can be accordingly provided.
However, for example when foreign substances (residual pieces of cutting metal or the like) adhere to the surface of a metal ring in a preceding process (solution treatment or the like) prior to the correction process, the foreign substances cut into the roller surface of the peripheral length correction device, consequently creating a problem by causing damage to the rollers of the peripheral length correction device. Additionally, if the impaired roller is used as is a number of defective metal rings with damaged surfaces will be produced. Consequently, this creates a problem of reduced production yield.